1. Field of the Invention
The present invention relates to a receiver, and more particularly, to a reliable co-channel interference canceler in a simulcast receiver and a method thereof.
2. Description of Related Art
In the United States, tests have been completed of a GA-ATV (Grand Alliance Advanced Television) system, which is a digital television transmission system standard which can replace the NTSC (National Television System Committee) standard. A GA-ATV (also called GA-HDTV or GA-VSB) receiver is standardized by the ATSC (Advanced Television System Committee) and adopts a VSB (vestigial side band) modulation method of digital transmission.
A new ATV signal is transmitted simultaneously with a conventional analog television signal (NTSC) via a TV channel which is currently not used in a given geographic region (also called is a xe2x80x9ctabooxe2x80x9d channel). Accordingly, the GA-ATV receiver must be designed to be robust against NTSC co-channel interference. The configuration of such a GA-ATV receiver is shown in FIG. 1, which is disclosed in U.S. Pat. No. 5,594,496, thus a detailed description of its operation will be omitted.
An NTSC interference rejection filter (hereinafter, called an NRF) selection controller 108 shown in FIG. 1 can be comprised of a field combfilter, a combfilter and a comparator which are shown in the above-described patent specification. The controller 108 can have a configuration disclosed in the following document [1]: [1] xe2x80x9cGuide to the Use of the Digital Television Standard for HDTV Transmission,xe2x80x9d pp.104-107, Doc.A/54, submitted to the United States Advanced Television System Committee, Apr. 12, 1995. Also, other configuration examples can exist.
Here, when a combfilter proposed by the aforementioned patent and an ATSC standard is adopted as an NRF 106, performance of removing NTSC interference is excellent. However, since the combfilter operates by subtracting two full gain signals, the power of additive white gaussian noise (AWGN) is increased by 3 dB. Also, when an 8-level input signal passes through the combfilter, the number of its output levels is increased to 15. Thus, a 3 dB SNR (signal-to-noise ratio) loss is incurred in the combfilter.
Meanwhile, the NRF selection controller 108 generates a selection signal for selecting a path having the smaller error among a non-NRF path and a path having passed through the NRF 106, and applies the selection signal to a selector 110, an adaptive equalizer 112, a phase tracker 114 and a trellis decoder 116. The selector 110 selects a signal (15-level) having passed through the NRF 106 or a signal (8-level) output by a block 104 without passing through the NRF 106, according to the selection signal. The adaptive equalizer 112, the phase tracker 114 and the trellis decoder 116 perform signal processing which is suitable for the state of the selected signal.
In the receiver shown in FIG. 1, selection of the NRF 106 by the NRF selection controller 108 is made prior to the adaptive equalizer 112, the phase tracker 114 and the trellis decoder 116, which means that the signal input to the NRF selection controller 108 includes not only co-channel interference but also AWGN, ghosting and phase noise. In order to solve this problem, in the aforementioned patent, a field combfilter filters a received signal including a field sync of sequential fields, to thus generate a subtracted signal in which static ghosting, DC offset and intersymbol interference have been removed. The NRF is selected according to the result of comparison of a combfiltered subtraction signal with a non-combfiltered subtraction signal, thereby removing the NTSC co-channel interference and other interference.
However, even in the above patent, moving ghosting and phase noise are not removed, which results in unreliable control of the NRF selection.
Meanwhile, as another existing co-channel interference canceler, a detector for detecting the NTSC co-channel interference over the entire section of received data without using a data field sync reference pattern is disclosed in U.S. Pat. No. 5,546,132. An NTSC interference rejection filter having a switched tomlinson precoder for reducing the NTSC co-channel interference in ATV receivers is disclosed in U.S. Pat. No. 5,602,583. A device for removing the NTSC signal interference using digital recursive notch filters is disclosed in the U.S. Pat. No. 5,325,188.
However, when HDTV broadcasting begins, it is inevitable that the NTSC and HDTV broadcasting formats will be in use simultaneously, and therefore a receiver must be capable of reproducing either format. That is, depending on geographic location, a particular TV channel may be broadcast in either NTSC or HDTV format, so a structure whereby either of the two formats can be watched is required. A receiver having the aforementioned structure is called a simulcast receiver.
Therefore, the simulcast receiver must reliably detect and remove the co-channel interference during reception of an HDTV signal.
It is an object of the present invention to provide a co-channel interference canceler which detects an existing analog broadcasting signal to determine whether co-channel interference exists, in a simulcast receiver.
It is another object of the present invention to provide a method of driving the co-channel interference canceler by detecting the existing analog broadcasting signal.
To accomplish the first object, there is provided a co-channel interference canceler in a simulcast receiver for receiving a high definition television (HDTV) signal having a digital format and an analog broadcasting TV signal, comprising: a detector for detecting a synchronous signal from the analog broadcasting TV signal and outputting a detection signal; a co-channel interference rejection filter for removing co-channel interference from a first input signal including co-channel interference and outputting a second input signal; and a selector for selecting either the first or second input signal according to the detection signal. Also, the detector of the present invention detects a reference signal from the analog broadcasting TV signal and outputs a detection signal.
To accomplish the second object, there is provided a method of removing co-channel interference for use in a simulcast receiver for receiving a high definition television (HDTV) signal having a digital format and an analog broadcasting TV signal, comprising the steps of: (a) detecting a synchronous signal from the analog broadcasting TV signal and outputting a detection signal; (b) canceling co-channel interference from a first input signal including co-channel interference and other interference and outputting a second input signal; and (c) selecting either the first or second input signal according to the detection signal. Also, in the step of outputting a detection -signal according to the present invention, a reference signal is detected from the analog broadcasting TV signal, and the detection signal is then output.